Separate names with a comma.
Gotta use at least 6 images.
I'd say whatever doesn't result in a scroll bar in one's signature is acceptable. Nothing irritates me quite like having my scrolling momentum severely hampered by a signature as tall as half the friggin' thread.
Just hold your cursor off to the side, bro.
Due to the changes with who can post signatures because of the new rank system, you may need to consult the User Rank thread first page for info on what size and amount.
Just saying, if your sig is so tall that it requires a scroll bar, then what is the point? That's just my 2 cents though.